How Neurologic Development Influences Gait Biomechanics and Pediatric O&P

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By Gerald Stark, PhD, MSEM, CPO/L, FAAOP(D)

Part 1 - The first of this two-part series addresses the developmental milestones that impact pediatric O&P care.

Children Are Not Small Adults

When clinicians treat pediatric O&P patients, it's important to remember that children simply cannot be treated as if they are small adults. The rules clinicians use for designing and fitting O&P devices need to be different because there are a number of intrinsic and extrinsic factors in children that often combine to present challenges and a greater degree of device fitting complexity than in adults.

Brian Giavedoni, MBA, CP/L, manager of the O&P Department at Children's Healthcare of Atlanta, agrees, "The most common clinical misconception is that children are just miniature versions of adults. I often hear clinicians commenting about adult amputees, comparing some of the issues they are having fitting pediatric patients, but the needs of children are just inherently different."

Joanne Kanas, DPT, CPO, FAAOP, director of rehabilitation for the Shriner's Hospitals — Florida, provides additional context. "Children are not just small adults. They are far more active, typically they have much longer wear times, and they have a number of people involved with their lives, such as parents, therapists, teachers, coaches, scout leaders, karate instructors, etc."

Bryan Malas, MPH, CO/L, director of Lurie Children's Hospital of Chicago, emphasizes the need for greater clinical flexibility. "Clinicians will want to treat children as adults and default to the same scripts they engage for adults, but these strategies don't always work as well. For example, it is critically important to not judge the patient based on their stature. I remember recently seeing a patient who was six feet, five inches tall, but he was only 11 years old. Just because he was as large as an adult, doesn't mean that he had the psychosocial maturity level to understand what was happening and to make choices."

One of the most profound differences in fitting the pediatric patient is that the goals and needs of the patient are a constantly moving target. The dynamic nature of the pediatric patient in terms of physical, mental, and personal development can change from month to month. Kanas says, "It must be remembered that children are continually growing, unlike adults. So they do not stay the same, and they need ongoing care that may change over time even though their diagnosis has not."

Musculoskeletal Growth Proportions

One essential element to consider when treating children is their growth and development, which are often evaluated with standardized distribution rates that differ from child to child. Compared to other primates, humans have a protracted development time, approximately 20 years, which is the lifespan of other primates.1 In that time the body will grow three and a half times in height, increase skin coverage seven times, and increase body weight 20 times.1

Body proportions also change with this development. Unlike adults, a child has a proportionally larger head and abdomen compared to appendages. For example, normally sized infants can barely touch their fingers over their heads, which would be a head the size of a beach ball in an adult. This is why the human infant is born in a premature state that allows the head's passage through the birth canal. Head growth occurs early; a child at age ten has a head 96 percent the size of an adult, with a majority of the growth in the limb segments.1

As a comparison, at one year old a child is four heads high; at four years, five heads high; at nine years, six heads high; at 16 years, seven heads high; and ultimately an adult is seven and a half heads high.1 There is also a sizeable variation in the growth of body parts. It has been shown that periods of growth last four to six months followed by bone thickening of four to six months.1

The body segments often alternate growth patterns. While the humeral sections of the arm are thickening, the radial section may be growing. This is why limb segments may look disproportionate in adolescents with larger feet and hands. The majority of growth in the arm is in the proximal humerus, distal radius, away from the elbow, while a majority of growth in the leg is concentrated in the distal femur and proximal tibia, toward the knee.2 (See Table 1.)

Until age six, limb growth is slow compared to body and head growth. Growth rates for boys and girls remain the same until age nine, and between the age of ten and 11, more height is gained through the growth of the limbs. Short young children grow more slowly over time.1 In adolescence, taller children grow more slowly and shorter children more rapidly for a longer period of time.3 At onset of puberty, typically between ten and a half to 11 years of age in girls, and 12 and a half to 13 in boys, children experience a remarkable growth rate that is maintained for about two years.3 Humans reach their final height at age 20 while their trunk may continue to grow until age 25.3

Developmental Biomechanics

A group of pediatric orthotists and prosthetists were recently asked what the unique qualities of pediatric gait are and how the clinicians accommodate the child with O&P devices. They smiled at the simplicity of the question and admitted that pediatric gait can be "all over the map." Alignment was described pragmatically, but vaguely, as "somewhere in the middle of where they are going." Although pediatric gait is individual in nature, it is literally a dynamic and moving target, not only physically, but developmentally as well. This is because neurologic development and biomechanics of mobility of the child are directly intertwined.

Malas suggests temperance when using these development guidelines. "I think these cognitive and ability timelines and milestones do have their place. So if a child is not showing certain timelines, then we can look at the possible causes and pathologies. The norms are important as a starting point, but you have to be balanced, and base your conclusions on what we are finding with the presentation and assessment."

Kanas adds, "These are ranges established with the norms that are documented. Keep in mind, similar to the K-levels, which were never developed for pediatrics, there are no norms for abnormal timelines. It is best not to focus entirely on certain goals or markers."

Coleen Coulter-O'Berry, PT, DPT, PhD, PCS, team leader of the Limb Deficiency Program Children's Healthcare of Atlanta, emphasizes the developmental milestones that are age-appropriate, "You really have to treat the child at the appropriate developmental age. You need to ask what would be age-appropriate with their peers developmentally rather than adhering to a strict timeline, she says. "It distresses me when I hear that a patient with cerebral palsy, for example, is not standing because they cannot sit independently. A child does not have to sit, to crawl, stand, or walk in that order, but should be they should doing what others their age are doing. Also we need to remember it isn't always the highest technology that answers these needs, but the most appropriate technology."

As with any other child milestones, neurologic development also depends on the interaction and involvement of their individual context and personality, such as reading to them, teaching them to self soothe, playing peek-a-boo and hide-and-seek, and providing safe but interesting places to explore. This may be more challenging with multiple involvements such as neurologic, hearing, sight, mobility, or congenital limb difference. The reason for developmental differences related to mobility and limb difference is that interaction with the environment is essential for brain development.

Previously it was thought that motor development increased with cognitive capacity, however now it is understood that it is motor development that drives neurologic development. Therefore, Kanas cautions, "You can risk developing ‘splinter skills,' which means you have worked and worked and worked on one particular skill that is unrelated to the developmental continuum. Every child is different, and they will develop with their own timeframe. Use the published timelines as info, but don't lock into them."

Developmental Timelines

At two months, children should be able to smile at people, briefly calm themselves with hands to mouth, and seek out the parent. They make volitional cooing and gurgling sounds and turn their heads to audio cues. They pay attention to faces, recognize people at a distance, and become bored if activity ceases. Physically they can hold their head up and begin to push up from the prone position.

At four months, children smile spontaneously and play with people while mimicking facial expressions. They watch faces intently and can respond to the emotions of others while reaching for toys. At this time, they can hold the head steady without support and can push down on hard surfaces with their legs. They can handle toys and bring them to the mouth. Typically, they can roll from the prone to supine position and push up with their elbows when prone. At this point, a passive upper-limb prosthesis can be introduced.

At six months, children can recognize familiar faces, especially their parents. They can recognize themselves in a mirror and respond to their own name. Language is forming. They begin to show curiosity in particular things and can pass an object from one hand to the other. They begin to rock back and forth, can crawl at times, can stand with support, and may bounce on the floor. This is when a lower-limb prosthesis can be articulated to help crawling and aid in locomotion.

At nine months, children's social awareness increases, and they may cling to parents and avoid strangers. They have favorite toys and can point at objects. They understand "no," and can say simple words while mimicking others. They can play peek-a-boo, recognize falling objects, and look for people who are hiding. Developmentally, they can stand while supporting themselves on other objects and sit confidently without support. Also they can pull to stand and crawl freely.

At one year, children have developed strong attachments to parents and can be very shy with strangers or healthcare workers they do not know. They show fear in some situations, but now enjoy stories, try to get attention, initiate peek-a-boo and pat-a-cake, and help to dress. They are exploring their environment fully and find things easily. They copy gestures and can use cups and hairbrushes. They also gesture by pointing at things and can interpret directions to physical action.

Children begin walking from ten to 18 months, but this varies greatly. Initially they present with significant genu varum (bowed legs) that are externally rotated to maximize stability.1 Biomechanically, toddlers are unstable and top heavy, learning to walk using basic motor skills while balancing the weight of their proportionally larger head. Imagine a shaky adult trying to walk with a head so large it was roughly one quarter their height. Initially the child's slow, short-stepped, stable gait, with little reciprocal arm motion, maximizes balance and provides protection in the event of a fall.3

When first learning to walk, less than 50 percent of children show the presence of a full heel strike, planting their foot immediately at midstance, but by 18 months most develop a heel strike.3 Gait and motor development at this stage progress exceedingly fast: At 12 months 95 percent can squat to stand, at 18 months 80 percent can run, and at 24 months 97 percent can run.3 For children, the high activity of running becomes the preferred mode of ambulation until their ambulation level slows and matures at the onset of adolescence. Children then continue to refine their gait and improve relative balance. At two and a half years, about 50 percent of children can stand on one foot for six seconds, but at three and half years most can hop for 50 meters.3 Coulter-O'Berry adds, "Knee centers in the developing child do not need to be equal initially. Completely symmetric and equal walking is not necessarily the goal. The real goal is allowing side sitting, crawling, half-kneel, tall-kneel, upright cruising, and then walking. The real limitation is finding the right sized prosthetic componentry that allows this."

At two years old, children can mimic speech and movement easily. They are much more independent, if not defiant, but can follow instructions.4 They can find hidden things and can name abstract things that are not present.4 They can stand on tiptoe, run, and kick a ball, as well as confidently climb on furniture, stairs, or playground equipment.4

At three years old, they can carry on a conversation and understand abstract words like in and on. They are now running quickly, pedaling a tricycle, and walking down stairs step-over-step.4 By four, they know their colors and numbers and can count.4 They also understand stories and know the concept of time. They can use scissors, begin writing, and play board games.4 They can hop and stand on one foot for two seconds, can catch a bounced ball, and can pour, cut, and mash their own food.4 At this age, children exhibit a smoother heel-to-toe adult gait, complete with reciprocal arm motion and narrow base of support.4

Finally, by five, they can do somersaults, hop, and stand on one foot for ten seconds. They easily use a fork and spoon and are confident with activities of daily living such as dressing, undressing, feeding, and toileting. They are constantly testing their physical capability with climbing, swinging on swings, and ball sports.4

Between seven and eight years old, children exhibit internally rotated limbs and genu valgum characteristics (knock knees) as a result of limb growth.3 Velocity and step length become more aggressive as well as the ability to change direction as motor skills gradually improve.

Of course these timelines are merely guides, and children will develop at their own pace. However, the timelines will help clinicians understand the speed at which the pediatric patient is changing, not only biomechanically but neurologically as well. The informed clinician uses the input of the parents and rehabilitation team to anticipate, rather than react, to future changes for the most optimal outcomes.

Look for part II of this article discussing pediatric componentry and clinical considerations in the January 2021 issue.

 

Gerald Stark, PhD, MSEM, CPO/L, FAAOP(D), is a senior clinical specialist at Ottobock Healthcare, Austin, Texas.

 

References

1.       Northwestern University Upper Extremity Prosthetic Manual. 2002. Northwestern University Prosthetics-Orthotics Center.

2.       Croney, J. 1981. Anthropometry for Designers (Revised Edition). Van Nostrand Reinhold, New York, New York.

3.       Winter, D. 2009. Biomechanics and Motor Control of Human Movement, 4th edition. Wiley-Interscience Publications, New York, New York.

4.       CDC's Developmental Milestones 2020. Center for Disease Control. doi: https://www.cdc.gov/ncbddd/actearly/milestones/index.html

5.       Peck, S. 1982. Atlas of Human Anatomy for the Artist. Oxford University Press, Oxford, England.

6.       Dreyfus, H. 1966. Anthropometric Data: Standing Adult Male & Female

7.       Cornell University Ergonomics Web. 2002. Cornell University. doi: http://ergo.human.cornell.edu.